I was East, playing SAYC, IMPS.
After 3NT failed miserably, the following conversation occurred:
W: You do not have the points to jump in diamonds.
E: I have 17 points.
W: I only count 15.
E: 15 HCP, plus 2 for the 6 card diamond suit.
W: Those points are worthless if diamonds are not trumps, you cannot count them. Especially when I passed initially; you must bid 2!d.
The most difficult part of discussions like this is you're never sure whether your partner is correct or has no clue at all, especially when your partner has specified their skill as 'Advanced' or 'Expert' (in my experience usually this has no correlation with skill).
To me 3!d seems like an obvious bid, and whether partner has passed or not has nothing to do with it.
PS - can someone point me to a thread explaining how to insert a hand diagram from a hand played within BBO? I found one from a couple of years ago but the instructions didn't appear to work very well, so I recreated this manually via the hand editor button.